Process for controlling case-hardening



PATENT oFFlcE.

WILLIAM H. ALLEN, or nETEoIT, MICHIGAN, 'AssI NoE To PARKER RUST-ROOF COMPANY, on DETEoIT, MICHIGAN, A CoEroR TIoN or MICHIGAN.

PROCESS FOR CONTROLLING CASE-HARDENIN G.

Patented May I0, 1921.

No Drawing. Application filed April 17, 1919, Serial No. 290,748. Renewed January 17, 1921. Serial T 0 all whom may concern:'

Be it known that I, WILLIAM H. ALLEN,

a citizen of the United States, and residing ticle of iron or steel may be limited by copper-plating suchsurfaces as are to remain soft before subjecting the article to the action of the carbonizing gases in the cementation or case-hardening chamber or receptacle.

It has also been known for some time that in order to perfectly rust-proof articles of iron and steel by the processes set forth in the patents granted to Coslett, No. 870,937, dated November 12, 1907, and to Richards, No. 1,069,903, dated August 12, 1913, that the metal must be clean in order to permit proper actionby the solution of ferric phosphate.

hen the surfaces of articles of iron and steel have been changed from metallic iron to ferro-ferric phosphate by the frust-' proofing processes described in the above named patents, cementation or case-hardening action is retarded, and when the rustproofing process is imperfect, the casehardening gases have ifect. I have discovered that when the articles are covered in whole or in part with an organic substance that is insoluble in aqueous slightly acid solutions, such as shellac and other varnishes, that the rust-proofing process described in said patents has no efi'ect on such coated areas.

I hare further discoveredthat when a rust-proofed surface is coated with a thin film of fused acid phosphates of sodium or potassium, or other salts, such as borax or borate 'of ammonia and soluble silicates, as are fusible at about the temperature within the case-hardening chamber, that the case-' hardening action is entirely prevented for such rust-proofed areas. happens that the fused salt enters the minute interstices of the ferro-ferric phosphate surface and I have also discovered that where certain areas of articles of iron and steel arecoated with shellac or other readily fusible organic material and the articles are rust'proofed, that when these articles are treated by the case-hardening were coated become case-hardened.

My present process consists in coating such surfaces of articles ofiron and steel as are to be case-hardened with an organic substance, such as varnish, which is insoluble in the rust-proofing bath, then treating the articles so as to change the noncoated surfaces from metallic iron to iron phosphates, and then subjecting these articles to the case-hardening process, with or without the intermediate step of coating the iron phosphate surfaces with a film of fused inorganic salt.

I claim process that the areas that v 1. Theprocess of hardening selected areas articles to the action. of case-hardening gases. 1

3; The process Ofhardening selected areas. of articles of iron and steel which consists in coating such 'areas with a material which may be disintegrated by heat but is insoluble in aqueous slightly acid solutions,

changing, the remaining areas from metallic iron to iron phosphates, coating the article with fused salts, and then subjecting the articles to the action of case-hardening gases.

4. The process of hardening selected areas of articles of iron and steel which consists in coating such areas with shellac, changing the remaining areas to iron phosphates, coating the articles with fused sodium phosphate, and thensubjecting the articles to the action of case-hardening gfses.

' ILLIAB ALLEN. 

